1. Field of the Invention
The present invention relates to a technique of operating an elevator in emergency by using a charged power supply in case that a power supply from a commercial main power source is shut down in an elevator system, and more particularly, to an apparatus for controlling an operation of an elevator in a power failure which is capable of minimizing discharge amount of a charged power supply when an elevator is operated on the charged power supply in emergency and of preventing an over current from flowing, and to its method.
2. Description of the Background Art
In case that an elevator car is unexpectedly stopped between floors during its operation due to a power failure, the car is supposed to perform an emergency operation toward nearest floor so as to have passengers get off therefrom.
In preparation for such a power failure, in order to supply a power to the elevator system, a power supply unit is additionally provided to a control board, and the power supply unit typically has a charger and a charging battery where tens of volt of direct current power supply is normally charged.
That is, when a power failure state that a main power is not supplied is detected by the power supply unit, a direct current power supply charged in the charging battery is converted to an alternate current power supply, which is then converted to an alternate current power supply having the same frequency as that of the main power supply via a step-up transformer and an inverter, and is supplied to an input terminal of a rectifier, according to which the elevator system is operated in emergency.
FIG. 1 is a schematic block diagram of an apparatus for controlling an operation of an elevator in a power failure in accordance with a conventional art.
As illustrated in the drawing, the apparatus for controlling an operation of an elevator in a power failure in accordance with a conventional art includes a main power supply inputting contactor 2 for supplying a main power supply 1 in normal state by being closed or for blocking a power input path from the main power supply 1 in power failure by being opened, a rectifier 3 and a smoothing condensor 4 for converting alternate current input from an main power source to a direct current and smoothing it, a discharging transistor 5 and a resistor 6 for limiting a charged voltage of the condensor 4 from rising to more than a predetermined level, an inverter 7 for inverting a direct current voltage outputted from the smoothing condensor 4 according to an output signal from a pulse width modulation signal generator 20 (to be described later) to an AC voltage, current detectors 8A, 8B and 8C for detecting a current supplied from the inverter 7 to an AC motor 9, the AC motor 9 driven by an output power supply of the inverter 7, a rotary encoder 10 for detecting a rotational speed of the motor 9 and outputting a pulse, a sheave 11 for receiving a driving force from a driving shaft of the alternate current motor 9 and winding or releasing an elevator car 13 in a vertical direction, a balance weight 12 connected to the elevator car 13, having a predetermined weight so as for the car to be balanced, and vertically operated in the opposite direction to the elevator car 13, a hall call button unit 14 for being pushed by passengers waiting on the hall of each floor and calling the elevator car 13, a car call button unit 15 for passengers in the elevator car 13 to select destination floors, a load detector 16 for detecting a load amount of the elevator car 13 a power supply unit 17 with a charger for emergency operation of the elevator in case of a power failure, an operation control unit 18 for controlling an operation of the elevator system according to a hall call from the hall call button unit 14 or car call from the car call button unit 15, a speed control unit 19 for outputting a speed control signal upon receipt of a speed command from the operation control unit 18, and a pulse width modulation signal generator 20 for outputting a pulse width modulating signal upon receipt of the speed control signal.
The operation of the apparatus for controlling an operation of an elevator in accordance with the conventional art constructed as described above will now be explained.
In a normal operation that the main power 1 is normally supplied to the elevator system, the operation control unit 18 generates a speed command b1 to operate the elevator according to a call from the hall call button unit 14 and the car call button unit 15, computes a weight difference between the balance weight 12 and the elevator car 13 on the basis of the load amount of the elevator car 13 detected by the load detector 16, and accordingly outputs a load compensation signal b2.
When the speed control unit 19 outputs a predetermined speed control signal to the pulse width modulation (PWM) signal generator 20 according to the speed command b1 outputted from the operation control unit 18, the pulse width modulating signal generator 20 controls the width of the pulse signal and outputs it to the inverter 7. Then, the inverter 7 accordingly controls a rotation speed of the alternate current motor 9.
The operation of the power supply unit 17 will now be described with reference to FIG. 2.
A main power supply failure detecting unit 17A monitors whether the main power supply 1 is supplied to the elevator system. When the main power is normally supplied to the elevator system, a battery voltage detecting unit 17G checks a voltage of the charging battery 17F, and if the voltage is lowered down to below a pre-set voltage level, the battery voltage detecting unit 17G drives a battery charging control unit 17I.
Accordingly, a predetermined pulse width modulating signal is outputted from the pulse width modulation signal generator 17K, and accordingly a voltage from the main power supply 1 is sequentially charged through a transformer 17C and a power converting unit 17D.
In case that the power failure detecting unit 17A detects a power failure state that the main power is not supplied to the elevator system, the main power input contactor 2 is turned off by a turn-off signal from a contactor drive unit 17B.
At this time, the AC power supply control unit 17J is operated so that the DC power charged in the battery 17F is converted to an AC power through the inverter 17D. Thus, the DC voltage from the battery 17F is inverted to an AC voltage having the same frequency as the voltage of the main power via inverter 17D, coils L1,L2,L3 and the transformer 17C and is outputted to the rectifier 3.
As the power failure detecting unit 17A detects the power failure and outputs a power failure detecting signal al to the operation control unit 18, the operation control unit 18 switches a normal operation mode to a power failure operation mode to perform an emergency operation. And, when the emergency operation is completed, the operation control unit 18 outputs an operation completion signal to the power supply unit 17, and accordingly, the operation of the power supply unit 17 is stopped.
Meanwhile, when the power supply unit 17 detects the power-failure and outputs a signal that the main power is not supplied to the elevator system to the operation control unit 18, the operation control unit 18 computes a weight difference between the balance weight 12 and the elevator car 13 on the basis of the load detect signal of the load detector 16.
In case that a weight of the balance weight 12 is heavier than that of the car 13, the operation control unit 18 determines that the running direction of the elevator car 13 is to be an upward direction, and in the opposite case, it determines that the operation direction of the elevator car 13 is to be a downward direction, and then outputs a speed command b1 to control the speed of the motor 9.
When the car 13 is started to be operated after its running direction is determined, the motor 9 is operated by an electricity generator, of which a generated energy is consumed as a heat by the discharging transistor and the resistor 6.
FIG. 3 is a detailed block diagram of the speed control unit of FIG. 1 in accordance with the conventional art.
Referring to FIG. 3, the process that the speed control unit 19 performs a speed control function according to the speed command b1 outputted from the operation control unit 18 will now be described.
When a current detector 19A detects a current detect signal corresponding to the current amount of each phase detected through each of the current detecting elements 8A.about.8C and outputs it to a current converter 19B, the current converter 19B converts it to a current of torque component and a current of magnetic flux component and outputs it.
A speed detector 19C detects a rotation speed of the alternate current motor 9 on the basis of a pulse signal outputted from the rotary encoder 10, and outputs a speed detect signal corresponding to the rotation speed.
A magnetic flux command generator 19D generates a magnetic flux component current command signal of the motor 9, and a magnetic flux estimator 19E estimates a magnetic flux from a magnetic flux component current outputted from the current converter 19B.
A subtractor 19F substracts an output magnetic flux of the magnetic flux estimator 19E from the magnetic flux command outputted from the magnetic flux command generator 19D and outputs a magnetic flux difference signal to a magnetic flux controller 19G.
The magnetic flux controller 19G outputs a magnetic flux component current corresponding to the magnetic flux difference signal outputted from the subtractor, and a subtractor 19H computes a compensating value of the magnetic flux component current outputted from the magnetic flux controller 19G to output it, and the magnetic flux current controller 191 outputs a magnetic flux voltage command in proportion to the difference.
Meanwhile, the subtractor 19J subtracts the rotation speed of the motor obtained by the speed detector 19C from a command speed represented by the speed command signal b1 inputted from the operation control unit 18, to output a speed difference signal.
Accordingly, the speed controller 19K outputs a torque current corresponding to the speed difference signal, and an adder 19L adds a load compensation current b2 inputted from the operation control unit 18 to the torque current, and outputs a corresponding torque current command.
A subtractor 19M subtracts an output torque current of the current converter 19B from the torque current outputted from the adder 19L and outputs an difference signal of torque component current, and a torque current controller 19N outputs a torque voltage command signal in proportion to the difference of torque component current
A slip frequency operator 190 computes a slip frequency according to a torque and a magnetic flux, and an adder 19P adds the computed slip frequency to the detecting speed of the speed detector 19C, and accordingly outputs a frequency command.
Then, a voltage converter 19Q receives a voltage command respectively outputted from the magnetic flux current controller 191 and the torque current controller 19N and the frequency command from the adder 19P, and generates a three-phase voltage command to output it to the pulse width modulation signal generator 20.
At this time, a power consumption P of the alternate current motor 9 and the torque Tq is expressed by the following equations (1), (2): EQU Tq=k.times.Iq (1) EQU P=Tq.times.Wr (2)
Wherein, k indicates a torque constant ##EQU1##
d: number of the magnetic pole, Lm: mutual inductance, Lr: leakage inductance, Xr: rotator magnetic flux), Iq indicates a torque current, and Wr indicates an angular velocity (rad/sec).
FIG. 4 shows a power consumption of the motor 9 when the elevator car is operated in a state that the balance weight 12 and the elevator car 13 are maintained to be balanced, in case that an abrasion between the hoist way and the sheave 11 is neglected.
When the sign of the rotation direction of the motor 9 and that of the torque current b2 are identical to each other, the power consumption has a positive (+) value in the equation (2), and in this case, since the motor 9 serves as a load, a power required therefor is to be supplied from the power supply unit 17, for which the power consumption should be smaller than the maximum capacity of the power supply unit 17.
Meanwhile, in case that the sign of the rotation direction of the motor 9 and that of the torque current b2 are not identical to each other, a power consumption has a negative (-) value, and in this case, the alternate current motor 9 serves as a power generator.
In this case, since the generated electric power is consumed as a heat through the discharging transistor 5 and the resistor 6, it is not necessary for the power supply unit 17 to supply a power to the motor 9.
As described above, when a power failure occurs, the moving direction of the elevator car 13 is determined by the operation control unit 18 in a manner that after the weight of the elevator car 13 is detected on the basis of the output signal of the load detector 16, the weight of the elevator car and that of the balance weight 12 are compared to each other, upon which in case that the weight of the car 13 is heavier than that of the balance weight 12, the operation direction of the car 13 is determined to be a downward direction, while in the opposite case, the moving direction of the car 13 is determined to be an upward direction, thereby operating the car 13 toward the nearest floor from the current position.
Accordingly, since the operation control unit 18 wholly depends on the output signal of the load detector 16 when determining the running direction of the car 13, if the load detecting by the load detector 16 is not accurate or is not in a good condition for a normal operation due to a malfunction, a problem arises in that the car 13 may be operated undesirably in the opposite direction to its proper direction.
FIG. 5 shows a case that the car 13 is operated by the DC power charged in the battery 17F of the power supply unit 17 when a power failure occurs.
When the weight of the balance weight is heavier than that of the elevator car 13 and thus the car 13 runs in the upward direction, a power consumption has a negative (-) value and the motor 9 is operated as a power generator. At this time, the generated energy is charged to the smoothing capacitor 4 through the inverter 7, so that the voltage across the smoothing capacitor 4 is increased.
When the voltage of the both ends of the smoothing capacitor 4 is increased to more than a pre-set reference level, the discharging transistor 5 is operated and the generated power is consumed as a heat through the discharging resistance 6, so that the generated power is not transferred to the power supply unit 17.
Accordingly, since the power supply unit 17 needs to supply the power only to the operation control unit 18 and the speed control unit 19, the discharging amount of the charging battery 17F is minimized.
Generally, the charging capacity of the charging battery 17F and the capacity of the power converting unit 17D are designed in a full consideration of the power consumption for accelerating and power loss due to an friction with a rail in a state that the balance weight 12 and the car 13 are balanced.
However, in case that the load detector 16 is malfunction and the operation control unit 18 misjudges the direction in which the elevator car should run (for example, in case of a misjudgement that the motor 9 is operated as a load), as shown in FIG. 6, the power consumption of the motor 9 becomes more than a rated value, and thus, an overcurrent flows to the power supply unit 17, resulting in that the circuit element is broken down or the discharge amount of the charging battery 17F is excessive, causing a problem that the elevator system would be stopped before the car 13 reaches the nearest floor.
Therefore, in case of a power failure, according to the apparatus for controlling the operation of the elevator of the conventional art, since the running direction of the car is determined only on the basis of the output signal of the load detector, if the load detector detects the load inaccurately, or a breakdown thereof occurs, the running direction of the car is not determined properly, and moreover, the elevator system is supposed to be stopped before the car reaches the nearest floor.